Frequency synthetizer for transmission of information to railway vehicles



Oct. 20, 1970 Q JAUQUET ET AL 3,535,510

FREQUENCY SYNTHETIZER FOR TRANSMISSION OF INFORMATION TO RAILWAYVEHICLES Filed June 19, 1968 2 Sheets-Sheet 1 Fig.1

INVENTORS Christian .IAUQUET Joseph CLAES ATTORNEY Oct. 20, 1970 JAUQUETET AL 3,535,510

FREQUENCY SYNTHETIZER FOR TRANSMISSION OF INFORMATION TO RAILWAYVEHICLES Filed June 19, 1968 2 Sheets-Sheet 2 AMPLIFIER FREQUENCYOSCILLATOR "I I C COMPARATOR 0 K- .3l T, PILOT OSCILLATOR T Fig. 2

INVENTORS Christian .IAUQUET Joseph CLAES ATTORNEYS Patented Oct. 20,1970 4 Int. Cl. B611 21/06 U.S. Cl. 246--34 8 Claims ABSTRACT OF THEDISCLOSURE This invention relates to a frequency synthetizer for use ina railway signalling system in which a cable located in each zone of arailway line is fed by currents of different frequencies depending onthe condition of the line in the zone following the zone where the cableis located. The frequency synthetizer comprises a chain of elements in aclosed loop including a number of oscillators of different frequencieseach of which is connected to a filter tuned to the correspondingfrequency through a gate which opens only when a signal voltage, isprovided by a signalling apparatus located in the zone following thezone under consideration. The outputs of the filters are fed to thecable through a summing amplifier and a power amplifier. The output ofthe power amplifier is applied to a comparison circuit which delivers anoutput signal only when the output voltage of the power amplifier isbetween two predetermined values. This output signal controls theopening of a gate which permits a pilot oscillator to drive an amplifierwhich feeds the above-mentioned frequency oscillators. .In addition,means are provided to initially open the gate associated with the pilotoscillator to initiate the operation of the circuit.

This invention relates to a frequency synthetizer for transmission ofinformation to railway vehicles.

It has been established that a train running at a speed of 200 km./h.requires a distance of at least 3 km. to come to a stop. The normalsignalling methods which are conceived for trains whose speed does notexceed 160 krn./h. do not permit to warn in time an engine driver of thepresence of a stop signal. Nevertheless, in order to permit trains torun at 200 km./h. on railway lines equipped with the normal signallingmethods without having to modify it, it has been proposed to position aspecial signalling device in the train which responds to the requiredconditions. For this purpose, a cable in the shape of a loop has beeninstalled between the rails in each railway zone. Such cable isenergized by currents of different frequencies according to thecondition of the signals at the entrance of the zone following the zoneunder consideration. This loop induces a voltage in the train whichdetermines the operation of the local signalling system. Thus, in a zonepreceding a red light, a first frequency is fed to the cable to signalthat the train must be stopped at the end of the zone. In the precedingzone, at the end of which is positioned an amber light, a secondfrequency indicates that when approaching the light the speed must bereduced under 160 km./h. In the two zones further ahead, Where greenlights are located, a third and a fourth frequencies corresponding to180 and 200 km./h. respectively are fed to the cable.

The object of the present invention is an apparatus called frequencysynthetizer whose function is to provide the cable of each zone with acurrent of a suitable frequency in accordance with the conditions on theline and this, with a maximum amount of security. The frequencysynthetizer in accordance with the invention comprises a chain ofelements in a closed loop including a number of oscillators of differentfrequencies each of which is connected to a filter tuned to thecorresponding frequency through a gate which opens only when a signalvoltage is provided by the apparatus controlling the signal located inthe zone following the zone under consideration. This voltage appearswhen the conditions on the railway line require the feeding of the cableof the zone at the said frequency. The outputs of the filters areapplied to the input of a summing amplifier which is connected to apower amplifier feeding the cable. The output voltage of the poweramplifier is applied to a comparison circuit which delivers an outputsignal only when this output voltage is between two predeterminedvalues. This output signal controls the opening of a gate which permitsa pilot oscillator to drive an amplifier which feeds the above-mentionedfrequency oscillators. In addition, means are provided to initially openthe gate associated with the pilot oscillator to initiate the operationof the circuit.

The invention will now be described with reference to the drawings whichrelate to a particular embodiment of the invention. In the drawings:

FIG. 1 indicates schematically the frequencies applied to the cableslocated in the successive zones corresponding to the representedpositions of the signals; and

FIG. 2 illustrates a frequency synthetizer in accordance with theinvention.

As indicated in FIG. 1, in a section preceding a red light a frequency Pis fed to the cable to signal that the train must be stopped at the endof the zone. In the preceding zone, at the end of which is positioned anamber light, a frequency F indicates that when approaching the light thespeed of the train must be reduced under krn./hr. In the two zonesfurther ahead, where green lights are located, frequencies F and Fcorrespond respectively to and 200 km./h. respectively.

FIG. 2 illustrates a frequency synthetizer associated with the controlequipment of a signal located down a railway zone equipped with atransmitting cable K. This signal comprises lights R, J and V which arerespectively red, amber and green and fed by a source of alternativecurrent AL through the contacts of relays R and R, which, with a thirdrelay R are controlled by logic circuits not shown. Relay R is energizedwhen the zone down the signal is free and relay R is excited when thezone down the preceding zone is also free. Relay R is energized when athird zone past the two preceding zones is also free. The positions ofthe contacts of the relays R R and R shown in FIG. 2 correspondrespectively to R, released and R and R energized.

The release of relay R determines the energization of light R and oftransformer T The release of relay R combined with the energization ofrelay R light up light I and energize transformer T The energization ofrelays R and R lights up light V. Finally, the energization and therelease of relay R can permit the energization of transformers T and Trespectively. The secondary windings of transformers T,, T,-, T and Tprovide information signals r, j, v, and p which involves the necessityof feeding cable K with frequencies F F F and F respectively. It isunderstood that only one of the above information signals is generatedat a time. The synthetizer comprises four oscillators F F F and Foperating, when energized, at the frequencies designated above by thesame notations. Oscillators F F and F are connected to filters f h and Frespectively through corresponding gates P P P and P These gates openonly when information signals r, j, v, or p are applied to them. Theymay be relays, magnetic static elements, or transistor circuits. Theoutputs of the different filters are connected to the input of an addingamplifier AS which drives a power amplifier AP whose output feeds cableK through a transformer T The output voltage of amplifier AP is applied,after having been rectified, to the input of a comparison circuit Cwhich delivers an output signal only when the above voltage lies betweentwo predetermined values. Such a comparison circuit is disclosed in US.patent application No. 591,546 filed in the name of the presentassignee. The output signal of circuit C opens a gate S which permitsthe energization, by means of a pilot oscillator O, of an amplifier AAwhich feeds the different oscillators F F F and F through a transformerT A push-button switch B permits the opening of gate S in the absence ofan output signal from comparison circuit C and starts the synthetizercircuit which continues to operate when push-button switch B is releasedassuming that the circuit works properly. In the example illustrated inFIG. 2, information signal r only is present and opens gate P so thatoscillator F which is fed by amplifier AA in turn feeds filter f whoseoutput causes the energization of cable K through amplifiers AS and APon the one hand, and on the other hand the energization of comparisoncircuit C which opens gate S permitting oscillator O to energizeamplifier AA which feeds oscillator F Consequently, the synthetizercircuit works in a closed loop and the breakdown of one of its elementscauses the stopping of the operation. In particular, an oscillatorcannot control the energization of the cable unless it is connected to afilter tuned to the same frequency through its associated gate.Consequently, a protection is secured against any drifts of theoscillator or the filter because it is recognized, and this isreasonable, that two breakdowns cannot happen simultaneously and thatthe equipment will take all its configurations between two successivebreakdowns. This is true because it happens at every passing of a trainand that, on the other hand, the average time interval betweenbreakdowns in an equipment of this type is in the order of six months toone year. The operation in a closed loop causes the stopping of theapparatus at the first breakdown which prevents a second breakdown fromcompensating the first one. For example, if a drift of oscillator F didnot stop the equipment, it would not be impossible that f starts also todrift towards the modified frequency off oscillator F in which case thecable could be fed at a frequency different from the normal frequency ofoscillator F The elements constituting the above frequency synthetizermay be built up in a known manner, furthermore, various modificationsmay be effected without departing from the scope of the presentinvention.

We claim:

1. A frequency synthetizer for use in a railway signalling system inwhich, in each zone of a railway line, signals of different frequenciesin accordance with the state of signalling lights at the entrance of thezone following the zone under consideration are inductively transmittedto the trains, comprising a chain of elements in a closed loopincluding:

(a) a cable forming a loop located along the railway line in each zoneand having two terminals;

(b) a plurality of oscillators operating at different frequencies;

(c) a plurality of filters tuned to the frequency of said oscillators;

(d) a plurality of gates, each gate interconnecting an oscillator to anassociated filter, each gate being opened by a signal from the railwayzone following the zone under consideration and such signal appearingwhen the railway line conditions require the energization of the cableof the zone under consideration at a predetermined frequency;

(c) amplifier means connected to the output of said filters forenergizing the terminals of the cable;

(f) a comparison circuit connected to the output of said amplifiersadapted to generate an output only when the output of said amplifiermeans is between two predetermined values;

(g) a pilot oscillator;

(h) gate means interconnecting said pilot oscillator to said pluralityof oscillators, said gate means being controlled by the output of saidcomparison circuit; and

(i) means for initially opening said gate means to start the operationof the synthetizer circuit.

2. A synthetizer circuit as defined in claim 1, further including asignalling system comprising a plurality of relays which are selectivelyoperated in accordance with the line conditions in the zone followingthe zone under consideration to provide a signal to each of saidplurality of gates.

3. A synthetizer circuit as defined in claim 2, wherein said signal isderived from a source of alternating current through the contacts ofsaid relays.

4. A synthetizer circuit as defined in claim 3, further including alight for indicating the conditions of the line in the zone followingthe zone under consideration.

5. A synthetizer circuit as defined in claim 3, further including atransformer for coupling said source of alternating current to each ofsaid plurality of gates.

6. A synthetizer circuit as defined in claim 1, wherein said amplifiermeans includes a power amplifier.

7. A synthetizer circuit as defined in claim 1, further including atransformer for coupling said amplifier means to said cable.

8. A synthetizer circuit as defined in claim 1, further including anamplifier and a transformer connected to the output of said amplifierfor coupling said gate means to said plurality of oscillators.

References Cited UNITED STATES PATENTS 3.,339,067 8/1967 Reich 246-34ARTHUR L. LA POINT, Primary Examiner G. H. LIBMAN, Assistant Examiner USCl. X.R. 328152

